Calculate time of concentration with the Kirpich equation from channel flow length and slope or elevation drop, in feet or meters, with results in minutes.

Optional settings

Related Calculators

Time of Concentration Formula

tc = K L0.77 Sโˆ’0.385, K=0.0195 (L in m), K=0.0078 (L in ft)

Variables:

  • tc is the Time of Concentration (minutes)
  • L is channel flow length: meters for K = 0.0195, feet for K = 0.0078
  • S is dimensionless channel slope (elevation drop divided by flow length); divide percent slope by 100

How to Calculate Time of Concentration?

The following steps outline how to calculate the Time of Concentration.

  1. First, determine the travel length (m). 
  2. Next, determine the slope. 
  3. Next, use tc = K L0.77 S-0.385 with K = 0.0195 for meters or 0.0078 for feet.
  4. Finally, calculate the Time of Concentration.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

travel length (m) = 9

slope = 10% = 0.10 (dimensionless)

Frequently Asked Questions

What is the Time of Concentration in hydrology?

The Time of Concentration in hydrology is the time it takes for precipitation to travel from the most distant point in a watershed to a specific point, usually the outlet. It is a critical factor in determining peak discharge rates for designing drainage and flood control systems.

How does slope affect the Time of Concentration?

Slope plays a significant role in the Time of Concentration. Steeper slopes lead to faster surface runoff, reducing the Time of Concentration, while flatter slopes result in slower runoff, increasing the Time of Concentration. The Kirpich formula directly incorporates dimensionless channel slope; its coefficient must match the length unit.

Why is it important to calculate the Time of Concentration accurately?

Accurately calculating the Time of Concentration is crucial for effective water management practices. It helps in the design of stormwater management facilities, determining floodplain boundaries, and ensuring that drainage systems are adequately sized to handle peak flows, minimizing the risk of flooding and erosion.

Can the Time of Concentration formula be used for any watershed?

Kirpich is an empirical channel-flow relation, not a universal whole-watershed travel-time equation. Additional overland-flow components or a documented low-slope adjustment may be needed. However, specific watersheds may require adjustments or different formulas based on their unique characteristics such as land use, soil type, and vegetation cover. It’s always recommended to consult with a hydrologist or engineer for the most accurate assessments.